A New 400K Distance Record Set in Quantum Cryptography

In Brief

A team from China has refined the measurement-independent quantum cryptography method, sending keys and data faster and farther away than other teams thus far.

Independence

Quantum cryptography, the use of single photons to deliver messages without leaks, has the promise to be the future of data security. And for a while, it really seemed like was…until someone found out how to hack the devices that use it. Thus, there has been a scramble to set up quantum cryptography that is independent of the devices themselves.

They still used the typical method used in quantum cryptography: Quantum key distribution, where a key and a classical message is relayed. The catch has always been sending the key using quantum methods, and sending it fast and secure.

Now, the team asserts that have have been able to send keys more than 100 kilometers at data rates measured in kilobits per second. At lower speeds, that can be stretched to more than 400 kilometers, and it uses a way that does not depend on how the photons are detected. This is called measurement-independent quantum cryptography.

Tamper-proofing Needed

To be fair, the team cheated a little: the method does not rely on the detectors, but on the photon transmitters, and those devices could still be hacked.

But there are arguments that transmitters can be tested in a safe laboratory before transmission in order to ensure they are not compromised. This makes measurement-independent quantum cryptography the best pursuit in the field.

A bigger concern has been manufacturers building quantum memory in either transmitters or receivers that store information before it is transmitted, which can be revealed to an eavesdropper during another transmission.

The thing with this “Trojan Hack” is that it would be impossible to detect, without destroying the device. Hua-Lei’s device cannot get around this. In fact, the only way to get around it would be to use each device only once, which is too expensive to be practical. Still, a step forward all the same.